JP5808119B2 - Model eye, method for adjusting optical tomographic imaging apparatus, and evaluation method - Google Patents

Description

  The present invention relates to a model eye, a method for adjusting an optical tomographic imaging apparatus, and an evaluation method.

  2. Description of the Related Art An optical tomographic imaging apparatus (Optical Coherence Tomography: hereinafter sometimes referred to as OCT) is known as an apparatus that non-invasively captures (acquires) a tomographic image of a living tissue (for example, an eye retina).

  In an optical tomographic imaging apparatus, a light beam is two-dimensionally scanned on a retina by a deflector, and the reflected light and backscattered light are measured by an interferometer. As a result, a three-dimensional image including information in the depth direction (longitudinal direction) is acquired.

  Conventionally, in order to improve the image quality of tomographic images acquired by OCT, efforts have been made to achieve higher resolution (higher resolution). The evaluation of the image quality (spatial resolution) of a three-dimensional image is based on a lateral resolution indicating a resolution in a direction orthogonal to the optical axis direction of the light beam emitted from the OCT and a vertical resolution indicating a resolution in the optical axis direction. It is done separately. Therefore, the methods for evaluating each spatial resolution are also different.

  The designed lateral resolution of the fundus image is determined by the beam spot diameter scanned on the retina in OCT and SLO (Scanning Laser Ophthalmoscope). Further, in the fundus camera, it is determined by the NA of the optical system.

  A model eye is generally used for such evaluation of the lateral resolution. The model eye is provided with a single lens or a plurality of lenses, and a resolution chart is provided on the surface corresponding to the retina. In an apparatus to be evaluated for lateral resolution, this pattern is imaged, and the contrast of light and shade (light / dark) of the pattern corresponding to each spatial frequency is calculated. Thereby, it is evaluated whether the desired lateral resolution is achieved in the device to be evaluated.

  For example, in the model eye disclosed in Patent Document 1, a lens is incorporated in a main body of a substantially cylindrical model eye, and a resolution chart is arranged at a fundus conjugate position at the time of eye examination by a fundus camera. This model eye is provided with a light diffusion reflecting member only on the back side of the chart, and the operator adjusts the focus with respect to the eye to be examined while monitoring this. The evaluation of the lateral resolution is performed in a focused state.

On the other hand, the vertical resolution δ of OCT is theoretically obtained as the half width of the coherence function of the interferometer. Specifically, it is calculated by the following formula.
δ = 2 · ln (2) · λ ₀ ² / (π · Δλ) (1)
λ ₀ is the center wavelength of the irradiation light source, and Δλ is the half width of the wavelength spectrum.

  In general, a low-coherence light source is used as an OCT light source. However, in order to reduce the value of δ, a light source having a large Δλ is also being developed. In recent years, there has been reported an example in which a longitudinal resolution with δ of about 3 μm is realized using a light source with Δλ exceeding 100 nm.

However, these are theoretical values only, and it is desired that the vertical resolution can be evaluated by measuring the actual value as well as the horizontal resolution. As described above, in the evaluation of the vertical resolution, there is no resolution chart used in the evaluation of the horizontal resolution. As an evaluation of the longitudinal resolution using actual values, there is known a method of measuring plant cells, multilayer films, etc. whose approximate order of size is known. In Non-Patent Document 1, a thin film in which TiO ₂ fine particles having an average particle diameter of 1 μm are dispersed in silicon is prepared, and the image quality of a tomographic image is evaluated by the size of each fine particle image.

JP 2002-165759 A

T. Ralston et.al. “Real-time interferometric synthetic aperture microscopy” Opt.Express (16) 2555-2569 (2008)

  The value of δ (OCT vertical resolution) obtained by the above equation (1) is based on the premise that the wavelength spectrum distribution of the light source is Gaussian. FIG. 7A is a graph showing a Gaussian light source spectrum distribution and a corresponding coherence function shape. In this case, Δλ is 50 nm and the derived δ is 6 μm.

  Here, for example, an SLD (Super Luminescent Diode) is often used as an OCT light source. However, the spectral distribution of SLD is often not Gaussian. FIG. 7B is a graph showing the spectral distribution of the SLD and the corresponding coherence function shape. In this case, the full width at half maximum of the coherence function shown in the graph on the right side of FIG. 7 (b) is not significantly different from the value of δ obtained by Equation (1), but the base is greatly expanded, and the sharpness is reduced. It will be in the state.

  Also, although depending on the OCT specifications, the vertical sampling interval is often only about a few μm in reality, so even if an attempt is made to evaluate the vertical resolution by obtaining the width of the measured coherence function. In many cases, the required accuracy cannot be obtained.

  The coherence function is a minimum unit for forming a vertical component of a tomographic image, and corresponds to a point spread function in an optical system that forms a two-dimensional image such as a camera. Therefore, the longitudinal component of the observed tomographic image distribution is obtained as a convolution of the actual scattering intensity distribution of the object to be inspected and this coherence function.

  Here, a profile of a tomographic image obtained when an object is measured by OCT having the coherence functions shown in FIGS. 7A and 7B will be described with reference to FIG. Here, the dotted line indicates an object having a rectangular periodic scattering intensity distribution. The thin line shows the profile of the tomographic image obtained by the OCT measurement having the coherence function shown in FIG. 7A, and the thick line shows the tomography obtained by the OCT measurement having the coherence function shown in FIG. An image profile is shown.

  As shown in FIG. 8, although the half-value width of the coherence function shown in FIGS. 7 (a) and 7 (b) hardly changes, there is a large difference in the contrast of the position corresponding to the high-frequency light in the image. As a result, the contrast at the position where the position in the depth direction is small (that is, shallow) is small. Therefore, δ (half-value width of the coherence function) used as an index indicating the vertical resolution is not necessarily valid as a value expressing the vertical resolution when the tomographic image is imaged.

  The present invention has been made in view of the above problems, and provides a technique capable of acquiring information for evaluating resolution in the optical axis direction of light emitted from an optical system of an optical tomographic imaging apparatus. For the purpose.

In order to solve the above problems, one embodiment of the present invention provides:
A model eye used to evaluate an optical system in an optical tomographic imaging apparatus that captures a tomographic image of the fundus,
A first optical member on which irradiation light from the optical system is incident;
The irradiation light from the first optical member is incident, and a second optical member in which the Ru plurality of layers having different scattering intensities in the optical axis direction of the irradiation light is formed,
The plurality of layers include
A first scattering layer formed by dispersing first fine particles having a refractive index different from that of a medium having transparency;
A second scattering layer formed by dispersing second fine particles having a refractive index different from that of the medium and the first fine particles in a transmissive medium;
Are alternately formed in the direction of the optical axis of the irradiation light .

  According to the present invention, it is possible to acquire information for evaluating the resolution in the optical axis direction of light emitted from the optical system of the optical tomographic imaging apparatus.

The figure which shows an example of the cross-sectional structure of the model eye 100 concerning this embodiment. The figure which shows an example of a structure of the optical system of OCT. The figure which shows an example of the brightness | luminance profile of a tomographic image. FIG. 4 is a diagram illustrating an example of a cross-sectional configuration of a model eye 100 according to a second embodiment. FIG. 6 is a diagram illustrating an example of a cross-sectional configuration of a model eye 100 according to a third embodiment. The figure which showed typically an example of the structure of the some layer 3 shown in FIG. The figure for demonstrating an example of a prior art. The figure for demonstrating an example of a prior art. The figure which shows an example of a structure of the optical system of OCT. The figure which shows an example of the tomographic image of the model eye 100 shown in FIG. The figure for demonstrating the adjustment process of the thickness of the dispersion compensation glass.

  Hereinafter, an embodiment of the present invention will be described in detail with reference to the accompanying drawings.

(Embodiment 1)
First, an example of a cross-sectional configuration of the model eye 100 according to the present embodiment will be described with reference to FIG.

  The model eye 100 is used for evaluating an optical system of an OCT (optical tomographic imaging apparatus) that captures a tomographic image of the fundus. More specifically, it is used to evaluate the resolution (vertical resolution) of the optical system in the OCT along the optical axis direction of the light emitted from the OCT.

  Here, the luminance of an image captured by OCT corresponds to the intensity of reflection / backscattering inside the subject (eye to be examined). In order to give brightness to the captured image, it is necessary to provide an appropriate scattering density at a predetermined position along the optical axis direction inside the subject (eye to be examined).

  Therefore, in the present embodiment, layers having different scattering intensities are formed along the optical axis direction of light in order to change this density regularly in a pattern along the optical axis direction of light. Thereby, in this embodiment, the structure equivalent to the resolution chart used at the time of evaluation of horizontal direction resolution (resolution to the direction orthogonal to an optical axis direction) is provided, and longitudinal direction resolution (resolution to an optical axis direction) is provided. Enable evaluation.

  In FIG. 1, the model eye 100 includes a lens 1, a glass substrate 21, a plurality of layers 3, and a cylindrical housing 5 that holds them. For example, the region 4 between the lens 1 and the glass substrate 21 is filled with air. In addition, this area | region may be filled with liquids, such as water, and may be formed with transparent solids, such as glass.

  Here, as a correspondence relationship between the model eye 100 and the (actual) eyeball, the lens 1 corresponds to the cornea and the crystalline lens, the region 4 and the glass substrate 21 correspond to the glass body, and the plurality of layers 3 include Corresponds to the retina. In FIG. 1, for convenience of explanation, the thicknesses of the plurality of layers 3 are shown larger than the actual thickness.

  The model eye 100 is provided with a lens 1 as a first optical member and a glass substrate 21 as a second optical member. Irradiation light is incident on the lens 1 via an OCT optical system, Irradiated light from the OCT optical system via the lens 1 is incident on the glass substrate 21.

  Here, a plurality of layers 3 are laminated on the glass substrate 21 in the direction opposite to the incident light incident side. The glass substrate 21 is configured such that irradiation light is sequentially incident thereon. A plurality of first scattering layers 31 and second scattering layers 32 are alternately formed in the plurality of layers 3. The first scattering layer 31 is composed of a first transparent medium (a medium having transparency), in which first fine particles are dispersed at a first concentration. The second scattering layer 32 is composed of a second transparent medium, in which second fine particles are dispersed at a second concentration.

Note that the first transparent medium and a second transparent medium, to the light source wavelength lambda _c of the OCT, for example, having a transmittance of 90% or more. Here, fine particles (first fine particles, second fine particles) having different refractive indexes are dispersed in a photo-curing material such as an ultraviolet curable resin, and are cured after being thinned. Thereby, the first transparent medium and the second transparent medium are formed. A dispersant may be used so that the fine particles do not aggregate or precipitate.

The particle diameter of the fine particles (first fine particles, second fine particles) is, for example, equal to the center wavelength λ _{c of the} light source used in OCT, or larger than λ _{c and} smaller than the thickness t of the scattering layer. Is desirable. If the particle size is significantly smaller than the center wavelength λ _{c of the} light source, scattering does not occur at a desired intensity. If the particle size is larger than the thickness t of the scattering layer, the layer boundary is a uniform plane ( This is because it does not become a curved surface.

  Examples of the material of the fine particles (first fine particles, second fine particles) include latex and silica particles, and have a refractive index different from that of the transparent medium (first transparent medium, second transparent medium). I just need it.

  In addition, the same particle size and material (refractive index) may be used for the first fine particles and the second fine particles, or they may be different from each other depending on the characteristics of cells in each layer of the actual fundus. A thing may be used. Further, when the material of both the fine particles is the same, for example, the particle size of the first fine particles is made larger than that of the second fine particles so that the scattering intensity in each layer is different. Further, when the particle diameters of both the fine particles are the same, for example, the number (or concentration) of the first fine particles is made larger (darker) than the second fine particles, and the scattering intensity in each layer is different. Make it.

  The first scattering layer 31 and the second scattering layer 32 do not necessarily have fine particles dispersed therein, and the first scattering layer 31 and the second scattering layer 32 are made of a single material. Also good. For example, the first scattering layer 31 and the second scattering layer 32 may be configured to include fine spherical bubbles in a single transparent material, or may be configured to be porous.

  When the concentration of the fine particles in the first scattering layer 31 and the second scattering layer 32 is too thin, the S / N of the image to be captured is deteriorated. Deteriorate. Since the signal intensity of the image to be captured also depends on the particle size, it is desirable to adjust the density so that it is comparable to the signal intensity of the image obtained when the actual fundus is observed.

  Here, the density of the first scattering layer 31 is adjusted so that the signal intensity of the obtained image is approximately the same as the intensity obtained when the pigment epithelium layer of the fundus is observed. The concentration of the second scattering layer 32 is adjusted to have the same intensity as when the inner net layer is observed. Further, in order to evaluate the resolution when the contrast is the highest, the particle concentration of the second scattering layer 32 may be made zero and transparent.

  In addition, if the reflectance at the boundary surface of each layer is large, the reflected light intensity from the boundary surface may be too strong, and the boundary peripheral region may not be imaged correctly. Therefore, it is desirable to use the same first transparent medium and second transparent medium in order to prevent reflection at the boundary surface due to the difference in refractive index between the two.

In addition, when different substances are used for the first fine particles and the second fine particles, different transparent media may be used according to the difference in their molecular structure in order to disperse them well in the transparent medium. In that case, to as small as possible reflectivity at the interface, the refractive index n ₁ of the first transparent medium (first scattering _layer), the refractive index n ₂ of the second transparent medium (second scattering layer) It is necessary to select a medium that minimizes the difference between the two.

The same can be said for the boundary surface 42 between the glass substrate 21 (refractive index n ₃ ) and the plurality of layers 3. As described above, when the concentration of the fine particles is set so that the signal intensity from the scattering layer is about the same as the signal from the fundus, the value of (scattered light intensity) / (irradiation light intensity) is about 10 ^−5. . It is desirable that the reflectance at each interface is below this value.

Here, the glass substrate 21, the transparent medium of the first scattering layer 31, and the transparent medium of the second scattering layer 32 are
{(N _j −n _k ) / (n _j + n _k )} ² ≦ 0.00001
Where j, k = 1 to 3, j ≠ k
Select a material that meets the requirements.

  Thereby, the influence on the image by the regular reflection light in each boundary surface can be reduced. In addition, a good image with few unnecessary components formed only by backscattered light from within each scattering layer can be obtained.

  Further, in order to be able to evaluate the maximum longitudinal resolution of the optical system in OCT, it is necessary to obtain a spatial frequency corresponding to at least the half-value width δ (μm) of the coherence function ideally obtained from the half-value width of the light source spectrum. There is. Therefore, the first scattering layer 31 and the second scattering layer 32 in the model eye 100 include layers having a layer thickness of δ (μm) or less. In order to increase the measurement accuracy, it is desirable to be less than δ / 2 (μm).

  For example, when it is desired to grasp only whether or not the resolution is performed by δ (μm), the thicknesses of the first scattering layer 31 and the second scattering layer 32 may be all δ (μm). It ’s fine. Further, if it is desired to evaluate the vertical resolution for each spatial frequency, the thicknesses of the first scattering layer 31 and the second scattering layer 32 may be different from each other.

  Here, a method for evaluating OCT using the model eye 100 shown in FIG. 1 will be described. FIG. 9 is a diagram showing an example of the configuration of an OCT optical system.

The OCT includes an observation optical system 91 including an object to be inspected and a reference optical system 92 in order to construct a tomographic image according to the principle of a low coherence interferometer. The optical path lengths in the observation optical system 91 and the reference optical system 92 need to be substantially equal. In addition, the total dispersion value in both optical systems, that is, Σ [−λ · {d ² n _k (λ) / dλ ² } · d _k ] (n _k is the refractive index of each part including air, d _k (Spatial distance of each part including air) must be equal. If this value is different, the coherence distance, that is, the width of the coherence function increases due to the difference in the propagation speed of light depending on the wavelength, and the vertical resolution decreases.

As a technique for compensating for this dispersion, for example, a technique is known in which the reference optical system 92 is provided with a dispersion compensation glass 6 having a dispersion equivalent to the value of dispersion generated in the observation optical system 91 including the eye. Variance value of the ocular optical system are the known, also uniquely determined thickness d ₆ of the dispersion compensation glass.

  Here, the light (measurement light) emitted from the SLD light source 12 is propagated through the fiber 71 and enters the coupler 11. In the coupler 11, the incident light is branched at a predetermined ratio, one is propagated to the observation optical system 91 via the fiber 73, and the other is propagated to the reference optical system 92 via the fiber 74.

In the observation optical system 91, a light beam (beam) is emitted from the end of the fiber 73. This beam is collimated by a collimator lens 10 and deflected in a two-dimensional direction by a scanner mirror 9. The deflected beam enters the model eye 100 through the eyepiece 8 and is condensed and scanned in the vicinity of the plurality of layers 3. Reflected light and backscattered light from each point of the plurality of layers 3 enter the fiber 73 through the lens 1, the eyepiece lens 8, the scanner mirror 9, and the collimator lens 10. Here, since the thickness d ₆ of the dispersion compensation glass 6 is determined on the assumption that the human eye is arranged in the observation optical system 91, if the dispersion amount of the model eye 100 is different from the dispersion of the human eye, The coherence function spreads and the vertical resolution deteriorates, making it impossible to evaluate correctly. Therefore, it is desirable that the dispersion amount of the model eye 100 is designed to be equal to the dispersion of the human eye.

  On the other hand, in the reference optical system 92, a light beam (beam) is emitted from the end of the fiber 74. This beam is collimated by the collimator lens 10, passes through the dispersion compensation glass 6, and enters the folding mirror 7. The folding mirror 7 reflects the incident light toward the original optical path. As a result, the reflected light enters the fiber 74 again through the same optical path as the incident light.

  The respective lights incident on the fiber 73 and the fiber 74 are combined by the coupler 11. The light (interference light) combined by the coupler 11 is propagated to the spectroscope 80 via the fiber 72. The interference light that has entered the spectroscope 80 is collimated by the lens and is split into light of each wavelength by the grating 14. The split light is imaged on the one-dimensional sensor 15 by the action of the imaging lens.

  The one-dimensional sensor 15 detects the light intensity corresponding to each wavelength and generates (converts) an electrical signal. The electric signal is sent to the control unit 13. The electrical signal is converted into a wave number and then subjected to Fourier transform, and is obtained as a scattering intensity with respect to a longitudinal position. By performing this for each scanned light beam position, a tomographic image and a three-dimensional image are obtained.

Consider the case where the center wavelength λ ₀ of the light source 12 is 850 nm and the half width Δλ of the wavelength spectrum is 50 nm. In this case, the full width at half maximum δ of the coherence function obtained by calculation is about 6 μm. Therefore, the layer thicknesses of the layers 3 of the model eye 100 are all 6 μm.

  Here, the first scattering layer 31 is formed as a transparent layer in which fine particles are dispersed at a predetermined concentration, and the second scattering layer 32 is a fine particle concentration of zero. For example, an image shown in FIG. 10 is obtained as the tomographic image of the model eye. Here, the scattering intensity information for the position in the depth direction (z) with the scattering layer surface direction x = 0 is acquired, and the luminance profile is displayed on the display as shown in FIG. That is, the display shows the relationship between the position information in the depth direction and the scattering intensity information.

At this time, luminance contrast value ΔD = (Dmax−Dmin) / (Dmax + Dmin)
Can also be displayed simultaneously to evaluate the resolution in the tomographic direction. As shown in FIG. 1, when the scattering layer is formed on a plane, the incident angle of the irradiation beam varies depending on the position (x) in the plane direction, so that the optical path passing through each scattering layer is different. Therefore, in this case, the coordinate (z) in the depth direction shown in FIG. 3 needs to be corrected.

  The vertical resolution in the OCT to be evaluated can be evaluated directly from the image information thus acquired.

As described above, since the dispersion of the observation optical system 91 is ideally constant, the thickness d6 of the dispersion compensation glass ₆ is uniquely determined. However, in reality, since a manufacturing error or the like occurs, the vertical resolution is reduced. best to become so, it is necessary to adjust the thickness d _6. Here, using a model eye 100 of the present embodiment will be described based on the configuration shown in FIG. 2 how to fine-tune the d _6.

  If the thickness of the dispersion compensation glass 6 in the optical axis direction is not appropriate, the coherence function spreads and the vertical resolution is degraded. Therefore, the dispersion compensation glass 6 is adjusted by the following procedure.

First, the thickness d ₆ of the dispersion compensation glass 6, is set to a predetermined value based on the variance of the design of the device. The configuration in FIG. 2 is basically the same as that in FIG. 9 except that the dispersion compensation glass 6 has a configuration in which two wedge-shaped prisms are in close contact with each other on an inclined surface. Therefore, the operator slides the glass 6 along the slope by operating an operation unit (not shown). Thereby, the thickness of an optical axis direction can be adjusted arbitrarily. At this time, the model eye 100 is installed at a position corresponding to the eye, and is arranged so that the beam is condensed at each position in the plurality of layers 3.

At this time, luminance contrast value ΔD = (Dmax−Dmin) / (Dmax + Dmin)
Are simultaneously displayed in real time, and the operator refers to this value and adjusts the thickness of the dispersion compensation glass 6 so that the value becomes maximum. For example, FIG. 11 shows the adjustment process. Before adjusting the thickness d ₆ of the glass 6, in the tomographic image, the intensity distribution profile of a certain x position is displayed in real time as shown in thin line. At this time, the value of ΔD is about 0.23, and the value is also displayed. The value of the △ D is, when gradually changing the value of d ₆ as best increases, the luminance profile distribution is as shown in the state shown in bold lines, △ value of D is about 0.54. In addition, you may comprise so that the control part 13 may perform this adjustment automatically.

  As described above, according to the model eye according to the first embodiment, layers having different scattering intensities are formed along the optical axis direction (incident direction) of the irradiation light from the OCT. Thereby, based on the information acquired by OCT, the resolution in the optical axis direction of OCT can be evaluated. Furthermore, the OCT optical system can be adjusted based on the evaluation. That is, information for evaluating the resolution in the optical axis direction of the light emitted from the optical system of the OCT (optical tomographic imaging apparatus) can be acquired.

(Embodiment 2)
Next, Embodiment 2 will be described. In the first embodiment, the end surfaces 43 of the plurality of layers 3 are boundary surfaces with the outside (air), but in the second embodiment, a case where the reflectance of light at the end surfaces 43 is considered will be described. .

  FIG. 4 is a diagram illustrating an example of a cross-sectional configuration of the model eye 100 according to the second embodiment. In addition, the same code | symbol is attached | subjected about the structure same as the structure of FIG. 1 explaining Embodiment 1, and the description is abbreviate | omitted.

  In addition to the configuration of the first embodiment, the model eye 100 according to the second embodiment is provided with a glass substrate 22. The glass substrate 22 is provided as a third optical member on the end surface (surface opposite to the surface on which irradiation light is incident from OCT) 43 of the plurality of layers 3. That is, the glass substrate 22 is provided at a position farther from the incident side of the second scattering layer 32a. The glass substrate 22 is made of a material having the same or small difference in refractive index as the transparent medium of the first scattering layer 31 or the second scattering layer 32. Thereby, the reflectance at the end face 43 is reduced.

  The boundary surface 44 where the glass substrate 22 is in contact with the outside (to the outside) becomes a boundary with air, but if the OCT is a confocal optical system, if the thickness of the glass substrate 22 is increased, the boundary surface 44 is Since it deviates from the imaging surface, the reflected light from the boundary surface 44 can be reduced. The same applies to the setting of the thickness of the glass substrate 21 relating to the reflection at the boundary surface 41.

  Further, the glass substrate 22 is configured such that the boundary surface 44 is inclined with respect to the optical axis in order to prevent regular reflection light from returning to the OCT side. Note that the boundary surface 44 may be configured by a predetermined curved surface. Further, the glass substrate 22 may be configured using the same material as the transparent medium of the first scattering layer 31 or the second scattering layer 32. In that case, if the layers are formed thicker than these layers (the first scattering layer 31 and the second scattering layer 32), it is possible to suppress the regular reflection light from returning to the OCT side as described above.

  As described above, according to the model eye according to the second embodiment, the glass substrate 22 having a predetermined thickness is provided on the surface opposite to the surface on which the irradiation light enters from the OCT. Therefore, similarly to the first embodiment, it is possible to suppress unnecessary reflected light from being included in the measurement result when performing evaluation and adjustment. Thereby, the resolution in the optical axis direction of the OCT can be evaluated with higher accuracy than in the configuration of the first embodiment, and the OCT optical system can be adjusted.

(Embodiment 3)
Next, Embodiment 3 will be described. FIG. 5 is a diagram illustrating an example of a cross-sectional configuration of the model eye 100 according to the third embodiment.

  In the model eye 100 according to the third embodiment, the surface of the glass substrate 21 opposite to the incident light incident side is formed as a spherical surface, and a plurality of layers 3 are provided behind the surface. In the plurality of layers 3, first scattering layers 31 and second scattering layers 32 are alternately stacked, and the second scattering layer 32 is formed of a transparent layer having a fine particle concentration of zero. ing.

  The first scattering layer 31 and the second scattering layer (hereinafter referred to as a transparent layer) 32 are formed with a uniform thickness, but the transparent layer 32a formed on the outermost side is the other transparent layer 32. The boundary surface 44 is formed in a spherical shape shifted with respect to the optical axis. Thereby, the regular reflection light from the boundary surface 44 does not return to a light beam incident at any angle of view.

  Here, the lens 1 and the glass substrate 21 constitute a compound lens, and the focal length of the compound lens is designed to be 22.785 mm, for example, according to the Gullland model eye specification. The light incident on the center of the lens 1 is collected on the rear surface 42 of the glass substrate 21.

The material of the glass substrate 21 is, for example, glass whose refractive index at a wavelength of 840 nm is n ₃ = 1.491477. As the transparent medium used in the first scattering layer 31 and the transparent layer 32, for example, an ultraviolet curable resin having a refractive index n ₁ = 1.49 at a wavelength of 840 nm is used. In this case, the reflectance at the boundary surface 42 is 2.5 × 10 ⁻⁵ %.

  FIG. 6 is a diagram schematically showing an example of the configuration of the plurality of layers 3 shown in FIG.

  As described above, layers are alternately formed on the boundary surface 42 of the glass substrate 21 in the order of the transparent layer 32 and the first scattering layer 31. Here, the transparent layer 32 and the first scattering layer 31 form a pair with the adjacent transparent layer 32 and the first scattering layer 31. Each pair of layers has the same layer thickness. In the case of FIG. 6, each layer included in the unit has the same layer thickness with two pairs as one unit. That is, a plurality of units having different layer thicknesses are arranged in the plurality of layers, and the layer thicknesses gradually increase along the optical axis direction of light. This is to enable measurement of the contrast value for each spatial frequency. Note that the units do not necessarily have to be two pairs at a time, and the units may be assembled in units of one pair, three pairs, etc., and the layer thickness may be changed.

  Here, when evaluating OCT with a half-value width δ of the coherence function obtained by Expression (1) of 6 μm, the layer thickness of each unit is 3 μm, 4.5 μm, 6 μm, and 9 μm from the boundary surface 42 side. .

  By capturing a tomographic image using the model eye 100 having such a configuration, it is possible to calculate the contrast value for each spatial frequency, so that it is possible to grasp to what frequency the evaluated OCT can be sufficiently resolved. Become.

  When a unit having a thick layer is arranged on the incident side, the amount of light reaching the unit having a thin layer arranged at a deep position along the optical axis direction of light is reduced. In addition, the intensity of the return light (reflected light, backscattered light) also decreases.

  Further, in the SD (Spectral-Domain) type OCT as described with reference to FIG. 3, the signal intensity decreases in principle as the position becomes deeper depending on the number of pixels of the one-dimensional sensor 15 to be used. Therefore, in this embodiment, in order to suppress a decrease in the measurement accuracy of the contrast value at a high frequency, a thin unit is disposed on the incident light incident side, that is, on the glass substrate 22 side.

  Note that, in the model eye 100 according to the third embodiment, OCT can be evaluated and adjusted as in the first embodiment. At this time, since the layer corresponding to the fundus has a spherical surface, more realistic evaluation and adjustment can be performed on the two-dimensionally scanned light.

  The above is an example of a typical embodiment of the present invention, but the present invention is not limited to the embodiment described above and shown in the drawings, and can be appropriately modified and implemented without departing from the scope of the present invention. .

  In addition, you may implement combining a part of structure of Embodiment 1-3 mentioned above. For example, also in the third embodiment, the first scattering layer 31 and the second scattering layer 32 having a predetermined concentration may be provided as the plurality of layers 3. In addition, the transparent layer described in the third embodiment may be used instead of the glass substrate 22 that covers the outside described in the second embodiment, or described in the second embodiment instead of the transparent layer described in the third embodiment. A glass substrate may be used. In addition, the same can be said for the method of setting the layer thickness.

Claims (12)

A model eye used to evaluate an optical system in an optical tomographic imaging apparatus that captures a tomographic image of the fundus,
A first optical member on which irradiation light from the optical system is incident;
The irradiation light from the first optical member is incident, and a second optical member in which the Ru plurality of layers having different scattering intensities in the optical axis direction of the irradiation light is formed,
The plurality of layers include
A first scattering layer formed by dispersing first fine particles having a refractive index different from that of a medium having transparency;
A second scattering layer formed by dispersing second fine particles having a refractive index different from that of the medium and the first fine particles in a transmissive medium;
Are formed alternately in the direction of the optical axis of the irradiation light . A model eye used to evaluate an optical system in an optical tomographic imaging apparatus that captures a tomographic image of the fundus,
A first optical member on which irradiation light from the optical system is incident;
A second optical member on which irradiation light from the first optical member is incident and a plurality of layers having different scattering intensities are formed in an optical axis direction of the irradiation light;
Comprising
The plurality of layers include
A first scattering layer formed by dispersing first fine particles having a refractive index different from that of a medium having transparency;
A second scattering layer a second fine particle made of the same material as the first fine particles in a medium having permeability was formed by dispersing is placed on exchange each other in the optical axis direction of the illumination light,
Wherein said first particles in the first scattering layer, the second fine particles in the second scattering layer, model type eye you characterized in that the particle size is different, or whose concentration varies. The particle diameters of the first fine particles and the second fine particles are as follows:
Same as the center wavelength of the irradiated light, or model of claim 1, wherein a is smaller than the thickness in the optical axis direction of greater than the central wavelength of the first scattering layer and the second scattering layer eye. The first fine particles and the second fine particles are:
The model eye according to claim 1 or 2, wherein one of the concentrations is zero. Refractive index n ₁ of the second optical _member, the refractive index n ₂ of the first scattering _layer, the refractive index n ₃ of the second scattering layer,
{(N _j −n _k ) / (n _j + n _k )} ² ≦ 0.00001
(J, k = 1 to 3, j ≠ k)
Eye model according to claim 1 or 2, characterized in that meet. Composing a pair with the first scattering layer and the second scattering layer adjacent to each other,
The pair of scattering layers is
The thickness in the optical axis direction is the same,
The plurality of layers are:
The model eye according to claim 1 or 2 , wherein one or a plurality of pairs are formed so as to have different thicknesses along the optical axis direction. A model eye used to evaluate an optical system in an optical tomographic imaging apparatus that captures a tomographic image of the fundus,
A first optical member on which irradiation light from the optical system is incident;
An optical member on which irradiation light from the first optical member is incident, and a plurality of layers having different scattering intensities in the optical axis direction of the irradiation light are formed, and a surface in a direction opposite to the incident side of the irradiation light A second optical member formed of a spherical surface;
Comprising
The plurality of layers are:
Model type eye characterized in that it is laminated in a shape covering a part of the spherical surface. A model eye used to evaluate an optical system in an optical tomographic imaging apparatus that captures a tomographic image of the fundus,
A first optical member on which irradiation light from the optical system is incident;
A second optical member on which irradiation light from the first optical member is incident and a plurality of layers having different scattering intensities are formed in an optical axis direction of the irradiation light;
Comprising
Among the plurality of layers, the layer provided at the end of the incident side and the opposite side of the front Symbol irradiating light to the optical axis of the illumination light, wherein a greater thickness in the optical axis direction than the other layers model type eye shall be the. A model eye used to evaluate an optical system in an optical tomographic imaging apparatus that captures a tomographic image of the fundus,
A first optical member on which irradiation light from the optical system is incident;
A second optical member on which irradiation light from the first optical member is incident, and a plurality of layers having different scattering intensities are formed in the optical axis direction of the irradiation light;
Among the plurality of layers, provided on the side surface and the opposite side of the surface before Symbol illumination light enters a layer provided at the end of the incident side and the opposite side of the front Symbol irradiating light to the optical axis of the irradiation light a third optical member to be
Model type eye characterized in that immediately Bei a. An optical system evaluation method in an optical tomographic imaging apparatus that captures a tomographic image of the fundus,
Obtaining a tomographic image of a plurality of layers formed on the model eye according to any one of claims 1 to 9 , and evaluating a resolution in a tomographic direction using image information obtained from the tomographic image. A characteristic evaluation method. An adjustment method of an optical tomographic imaging apparatus,
Irradiating means irradiating measurement light to the model eye according to any one of claims 1 to 9 via an optical system;
A sensor acquiring scattering intensity information obtained from the model eye by the irradiation;
Adjusting the optical system based on the scattered intensity information. An adjustment method for an optical tomographic imaging apparatus, comprising: The method for adjusting an optical tomographic imaging apparatus according to claim 11 , further comprising a step of displaying a relationship between the acquired scattered intensity information and position information in the depth direction.

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